Better Buildings: Better Business Conference3/3/2017

This project was supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through the Conservation Applied Research and Development (CARD) program.

Research Update:

Rebecca Olson Neighborhood Energy Connection

Ben SchoenbauerCenter for Energy and Environment

Introduction to Hydronic Heating

Introduction to Hydronic Heating

• Non-condensing vs. condensing– Conventional boiler: condensation of combustion gases can rust out

heat exchanger– Condensing boiler: condensation of combustion gases is optimum for

efficiency

• Difference in return temperature requirement– In order to get combustion gases to condense, the return water

temperature needs to be below ~130°

• Radiator types– Radiator types and size play a significant role in the ΔT between

supply and return temps.

• Issues with replacement from one to other– It’s important to optimize efficiency when replacing a

conventional boiler with a condensing boiler based on the above factors

Hydronic Heating in MN

• Approximately 30% of MN homes are heated by a boiler

• Most of these are in older cities like St. Paul and Minneapolis

• Some in northern locations where central A/C is in less demand

Condensing Boilers

• How it works:– 2nd condensing heat

exchanger

– Less waste heat up the chimney

– If return water temp is low, more heat is exchanged from the combustion gases to the boiler water: increasing efficiency

– Supply temperature, flow rates and radiator type/size dictate return water temp.

Need for Condensing Boiler Research

• Lack of modulating condensing boilers in residential market

• Evidence that HVAC contractors and utilities have inconsistent confidence in products

• Prior research showing how important return temperature is on condensing boilers—commercial and hydronic air handler studies

• Need for quality installation protocol for utility savings and cost benefit confidence

Contractor Hesitance and Cost

• Cost of condensing units is generally high and variable

• $6,500--$15,000 installation cost range

• Lack of confidence in operation at high efficiency

• Issues with early models and maintenance callbacks

• Confusion about supply set-temps and condensing rate optimization

• Not as many model options in this market as condensing forced air systems

Prior Research and Information

• Conclusions:

– Return water temp is a primary factor

– Flow rates can influence return water temperature

– Outdoor reset needs to be installed and set-up properly

– Needed more info pertaining to MN housing stock, radiator types, and climate as well as more field implementation guidelines

• Building America—Butcher/Arena

• Commercial Boiler study—CEE Russ Landry

• ASHRAE Handbook

Prior Research and Information

Research Project Structure

• Field and Market research

• Existing condensing boiler monitoring

• Draft retro-commissioning activities

• Monitor savings after retro-commissioning

• Development of Quality Installation Protocol for Utility rebates based on savings from retro-commissioning

• Work with contractors to install condensing boilers in homes using QI protocol

• Information dissemination through webinars, presentations and published reports

Research Project Timeline

Task Name

1 Assessment

2 Existing boiler monitoring

2.2 Exisiting monitoring

2.3 recommissioning

2.4 Post monitoring

2.5 refinement of recommissioning checklist

3 New boiler installation

3.2 Installation

3.3 Monitoring

3.4 refinement of installation checklist

4 Final report

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

Market Research Structure

• Interview HVAC contractors about installation• Procedures

• Pricing

• Barriers

• Incidence

• Interview homeowners about performance• Comfort

• Maintenance

• Issues

• Interview Utilities about rebate development and rationale

Early Market Research Results

• Interview HVAC contractors about installation• 6 companies interviewed so far including a supplier• Low volume of boiler replacements and even lower volume of

condensing• Some hesitation on cost vs. performance• Costs seem to be inconsistent with equipment and labor details

• Interview homeowners about performance of existing condensing Boiler• Comfort is very high in existing sites• Maintenance does not seem to be an issue with any of the sites • Most sites relied on contractor to choose model• All 6 residents said they would recommend condensing system to others

• Interview Utilities about rebate development and rationale• Preliminary discussions indicate some utilities were worried about cost

effectiveness.• They may be getting high installation cost estimates, and not have a lot of

confidence in the efficiency

Field Research Phase I

• Characterization of Typical MN households• Based on aggregate consumption data from existing programs

• Participant solicitation/selection

• 6 sites chosen with existing modulating condensing boilers installed within the last 5 years

• Sites have varied heating loads and construction characteristics

• All homes have cast iron radiators• Some have other convector types, (i.e. baseboard, in-floor, low mass)

• 3 sites have indirect water heaters

• Monitoring• Gas usage

• Supply and return water temperature

• Flow rates

• Condensation rate

Field Research Phase I

• 1st half of 2015/2016 heating season, monitored as installed

• Made minor changes to optimize efficiency

• Adjusted supply temp

• Optimized turn-down ratio

• Attempted to change DHW supply temp and flow rate

• 2nd half of 2015/2016 heating season, monitored after adjustments

• Measured savings from 1st half to 2nd half

• Developed draft quality installation protocol

Site Selection Criteria

• At least 1 home per typical heating load quartile (420 to 700, 700 to 830, 830 to 1275, and >=1275 therms/yr)—based on MN aggregated residential utility program data

• At least 1 of each of the top 3 manufacturers—identified by utility rebate and local sales info

• A variety of installers

• MN program databases suggest between 30-36% of condensing boiler installs had indirect water heaters

• National Grid study found 30-40% of outdoor reset were not installed or installed poorly

• A variety of emitter types. Cast iron radiation, Low mass radiation, baseboards, and in-floor heating

Site Selection and Recruitment

• 17 recruited homes had smaller loads than typical homes (Avg 720 therm/yr)

– In selected 6 sites, larger usage homes were slightly under represented

• Identified 6 different manufacturers in recruitment.

– Top brands based on supplier and utility rebate data are represented in 6 selected sites

– Triangle tube, Buderus, Bunham, Weil Mclain all included

• 11 different installers in recruited homes

– 5 different installers in selected sites

Monitoring Set-up

Gas useFlow

Temp

Temp

Output

Temp

Temp

Runtime

Phase I Pre Retro-commissioning Daily Measured Performance

Daily Measured Performance

Phase I: As-found performance

Site Mode

Space

Heating DHW Combined

Space

Heating DHW

therms/yr therms/yr

d215_ex_02 As-found 837 na na 88.4% na

d215_ex_03 As-found 536 112 88.0% 90.5% 76.1%

d215_ex_05 As-found 88.0% 91.6% 70.3%

d215_ex_06 As-found 669 na na 95.1% na

d215_ex_07 As-found 731 na na 89.0% na

Annual Energy Use Annual Efficiency

459 94

Retro-Commissioning Actions

• Lowered Supply Temperature– Determined reasonable level to still meet load, but

lower return temp. to optimize efficiency

• Adjusted overall Reset Curve– Maximum supply temperature output at -12° vs.

default of 0°– This will lower the slope of the curve making more

points along the curve in the condensing mode

• Adjusted DHW Supply when possible– Based on lower efficiencies of indirect tanks as well as

indications of unused capacity– This was either impossible, or didn’t actually have an

effect on the return temp because of heat exchange capability

Phase I Site Example (D215_ex_07)

• Boiler for space heating only

• 6 Cast iron radiators

• 2 low mass radiators

• 3 zones w/ 3 t-stats

Min Max

28,500 99,000

at 140 Sup T at 180 Sup T

35,000 65,000

Capacity Estimates and Ratings (Btu/hr)

Boiler Output

Emmiters

Design Heating Load

(Bill Analysis)

at -12 F OAT

38,500

Supply Temperature Optimization

• Calculate or estimate the home heating load

• Calculate or estimate the emitter capacity

• Minimize the supply water temperature so that the house load can still be met

Phase I Site Example (D215_ex_07)

At 0 °F the house needs ~25,000 Btu/hr

Site Example(D215ex07)Emitter Capacity

130°F will deliver the needed 25,000 Btu/hrat 0°F OAT.

Site Example(D215ex07) Improvement

After retro commissioning performance

Add figure

Site Example (D215_ex_03) - DHW

• Boiler and indirect

water heater

• 6 Cast iron radiators

• 41 Gal WH set at 130°F

Min Max

22,745 75,200

at 140 Sup T at 180 Sup T

22,234 41,997

Design Heating Load

(Bill Analysis)

at -12 F OAT

28,925

Capacity Estimates and Ratings (Btu/hr)

Boiler Output

Emmiters

Site Example (D215 ex 03)

DHW Optimization

• Does the current DHW capacity meet load?

• Minimize the supply water temperature

– Many older boilers fix the DHW temperature

• d215_ex_03

• Minimize the DHW loop flow rate

– Manual pump adjustment

– Or boiler settings

Site Example (D215 ex 03)

After retro commissioning performance

Pump Speed DHW GPM Return Water T Capacity (Btu/hr) Avg Eff

As-Found High 2.8 133 53,100 76.1%

Opt_1 Med 2.5 131 49,300 77.3%

Opt_2 Low 2 129 45,500 77.9%

Comparison Chart

Site Mode

Annual

Combined

Eff

Annual

Space Eff

Annual

DHW

thermal

Eff

d215_ex_01 As-found 82.6% 86.2% 62.6%

d215_ex_01 Opt - OAT Curve

d215_ex_02 As-found na 88.4% na

d215_ex_02 Opt - OAT Curve na 90.2% na

d215_ex_03 As-found 88.0% 90.5% 76.1%

d215_ex_03 Opt- Clean 88.2% 90.5% 77.1%

d215_ex_03 Opt - DHW 1 88.4% 90.5% 77.3%

d215_ex_03 Opt - DHW 2 88.6% 90.5% 77.9%

d215_ex_05 As-found 88.0% 91.6% 70.3%

d215_ex_05 Opt- NA

d215_ex_06 As-found na 95.1% na

d215_ex_06 Opt - NA

d215_ex_07 As-found na 89.0% na

d215_ex_07 Opt - OAT Curve 90.4%

Analysis On-going

No Optimization to be Done

No Optimization to be Done

Conclusions Optimization

• Enabling recommended OAT reseat curve will achieve majority of savings

– Further optimization is possible, but not typically cost effective

• Water heating has room for improving efficiency

– However the system must be designed for low water temperatures (which appears to be uncommon)

Field Research, Phase II

• Selected 7 homes looking to replace non-condensing boiler with condensing boiler

• Used similar solicitation and selection criteria to Phase I

• Worked with 4 contractors to install new boiler in accordance with draft QI protocol in selected sites

• Monitoring (same as existing sites)• Gas usage

• Supply and return water temperature

• Flow rates

• Condensation rate

• Measure efficiency and compare to Phase I to estimate potential savings associated with QI protocol

Phase II Set-up Procedure leading to QI guide

• Boiler sized according to manual J– Ensure minimum firing rate is as low as possible

• Ensure outdoor reset is installed and meets manufacturer specifications.– Ex. Not located in sunny location or in exhaust path

• Set appropriate reset curve

Comparison Chart Phase II

Comparison of Annual Space Heating Efficiency

• On average condensing boilers saved 14% annual space heating costs over 80% AFUE boilers.

• Indirect water heaters were equivalent to a 0.70 EF power vent WH

Preliminary Conclusions

• Condensing equipment meet expected savings– Even boilers with non-aggressive reset curves are

efficient because set temp is reached before supply water temp gets to high limit

– 1-3% savings potential based on intensive set-up procedure—emitter capacity measurement

– Not cost effective

• DHW performance is more aligned with Power vented water heater than condensing– Not recommending unless cost competitive with

power vent

Dissemination Plan

• Hold several webinars and live presentations about project findings

• Work with contractors involved in interviews as well as installations to adopt QI protocol and hone in on pricing

• Work with WX agencies to determine assessment protocol for condensing boiler work scope

• Work with gas utilities not currently offering rebates for mod cons to implement rebate with QI protocol required

• Publish final research report and send out with DER newsletters etc.

Future plans

• Analyze cost effectiveness

• Finalize optimized reset curve recommendations

• Communicate with utilities about Basic set-up protocol

• Get information out based on Dissemination plan

• Publish final research report and send out with DER newsletters etc.

THANKS

This project was supported in part by a grant from the Minnesota Department of Commerce, Division of Energy Resources through the Conservation Applied

Research and Development (CARD) program.

Ben SchoenbauerSenior Research Engineer

Center for Energy and Environment

bschoenbauer@mncee.org

612-244-2413

Rebecca OlsonResidential Energy Program Director

Neighborhood Energy Connection

rebeccao@thenec.org

651-789-5705